New Tsumeb Update 30 July 2021

30 July 2021

WE continue our update today with 21 more fascinating Tsumeb specimens, all either thumbnails or miniatures. The selection includes some rare and outstanding species which may just fill the odd gap in a comprehensive Tsumeb collection.

On Tuesday we discussed the Tsumeb orebody, a pipe-like structure descending from the surface to over 1400 m deep. Its diverse mineralogy results from the interaction of its complex structure, the solubility of the host rocks, multiple phases of metal rich fluid entry and the interaction of meteoric water with not only the near surface upper levels, but much deeper parts not normally accessible from the surface. Meteoric water is derived from precipitation (rain) and tends to be oxygen-rich and slightly acidic.

The carbonate rocks which composed much of the Tsumeb orebody were gradually dissolved through the action of acidic water to produce a karstic environment, that is, one formed by the dissolution of soluble rocks. Once metals had been precipitated within the resultant void space, three major zones were subsequently oxidised through interaction with meteoric water. The 1stOxidation Zone was between surface and 11 Level. The 2nd Oxidation Zone, between 24 and 35 Level, from meteoric water entering via the North Break Zone (NBZ), a deep permeable fracture extending back to ground surface. The 3rd Oxidation Zone extends from 42 Level downwards and although not as strongly oxidised, likely connects back to the NBZ via open stress fractures, permeable faults and dissolution pathways.

Highlighting some of today’s choices, we have to begin with a showstopper. Scorodite is a rare mineral at Tsumeb and is seldomly seen amongst collections or even to buy. Do look at this fine divergent array of bladed Scorodite crystals as it is a large and magnificent example for Tsumeb. Translucent to opaque mid inky-blue to bluish-teal Scorodite crystals measure up to around 2.3 cm and form a splayed cluster measuring to 3.4 cm overall. The next miniature to catch my eye is a vibrant peppermint green Zincolivenite forming excellent lozenge-shaped crystals up to 0.9 cm wide and although all adjacent to one another, display as clear individual crystals. The prism sides are bright, light emerald green with peppermint green terminations plus several tiny balls of acicular dark green Olivenite cluster towards one end.

Both Melanotekite and Leadhillite are rare species at Tsumeb and in this miniature you get the two! Several micro-circular yellow brown Melanotekites (lead silicate) are seen embedded in a part formed crystal of lustrous colourless to grey Leadhillite. Several pale lemon yellow Mimetite crystals are also scattered over and embedded in the Leadhillite. The Melanotekite has been confirmed by EDS (Energy-Dispersive X-ray Spectroscopy) at the Royal Ontario Museum, whose study card accompanies this specimen.

Another Tsumeb rarity is Schultenite, a hydrogen bearing lead arsenate. In this small miniature the Schultenite forms white to colourless cleavages measuring to 9 mm towards one end of bright green intergrown Zincolivenite crystals.

Today’s selection contains two great Dioptases, one of Tsumeb’s most iconic species. The smaller of the two is an outstanding thumbnail composed of two large intergrown Dioptase crystals on a mini-dome of creamy white Calcite crystals. Despite its size, this specimen packs a lot of punch! Each crystal measures close to 1.2 cm along face edges, making them large for the species and appearing very large on this small yet perfect Calcite matrix.

The selection contains three very different Azurites, one of great form and complexity with Malachite, Wulfenite, Rosasite, Smithsonite and Bayldonite. Another is an ex-matrix elongate Azurite cluster displaying multiple growth crystals of a gorgeous rich azure blue, quite often showing large areas of the most sought-after electric azure blue once the lighting is just right. Exact measurements are difficult in such a complex crystal structure, but it is fair to say the main stepped crystal is about 5.5 cm long. The third is a superb pair of razor-sharp Azurite crystals attached to a thin veneer of microcrystalline sugary Cerussite and Dolomite. The semi-lustrous surfaces of the Azurite have begun the process of pseudomorphing to Malachite, but only just, resulting in a very attractive mottled mixture of dark inky-blue, leaf and olive-greens, light grey and partially iridescent steel-blue.

And how about an Anglesite? This is one of those specimens which just makes you smile in quiet appreciation of something rather special. Various sized, broad and flattened translucent smoky-cream Anglesite crystals emerge from a matrix of brecciated granular Anglesite and metal sulphides. The crystals have sharp Roman-sword terminations with vertically striated faces, some of which are coated in a fine film, possibly a sulphide coating just a few atoms deep, that impart a slight bluish cast.

Before concluding, let’s just give quick mention to a few other beauties. Creamy white Hydrocerussite coating a razor-sharp Cerussite crystal; a tangled mat of terracotta-orange Ludlockite crystals on a Germanite matrix; a cluster of dodecahedral Pyrite crystals and a classic Bayldonite pseudomorph after Mimetite with Azurite. The latter displays vibrant leaf green Bayldonite, partly to completely pseudomorphing and epimorphing intergrown prismatic crystals of Mimetite to 2.4 cm long.

Every mineral collector or mineralogist likes to create their own Top Ten global locations and one can almost guarantee Tsumeb is amongst most. The Mineralogical Record’s famous ‘Tsumeb!’ issue back in 1977 (was it really that long ago!?) was subtitled ‘the world's greatest mineral locality’. We at Crystal Classics adore Tsumeb for its rich history, geology and mineralogy and are proud to stock so many beautiful and amazing specimens. Have a good look through today’s picks, you could even imagine you’re on a virtual underground tour! Enjoy and we hope you find something you like. PT

Here is what you have to look forward to in next week's update:

Tuesday 3rd August & Friday 6th August - August New Finds

                                         

If you'd like to see a video of any of the specimens listed above then please contact us at orders@crystalclassics.co.uk and we'll be happy to assist you. We endeavour to respond to all enquires within 24 hours during weekdays, however at the weekend it might take us a little longer to respond.

 

DATES FOR YOUR DIARY

Crystal Classics, and our sister company UK Mining Ventures, will be in attendance at the following shows for the remainder of 2021:

AUGUST 13-15
East Coast Gem, Mineral and Fossil Show 2021
Better Living Center, Eastern States Exposition, 1305 Memorial Drive, West Springfield, MA 01089, USA

SEPTEMBER 10-18
Colorado Mineral and Fossil Fall Show 2021
Crowne Plaza Denver Airport Convention Center 15500 E 40th Ave, Denver, CO 80239, USA

SEPTEMBER 16-19
Hardrock Summit 2021 - Evolution
Colorado Convention Center, Four Seasons Ballroom 700 14th St, Denver, CO 80202, USA

OCTOBER 9-10
The Bakewell Rock Exchange 2021
Lady Manners School, Bakewell, Derbyshire DE45 1JA, UK

OCTOBER 22-24
The Munich Show 2021
Exhibition Center Messe München, WEST Entrance, Munich, Germany

NOVEMBER 20
The Sussex Mineral & Fossil Show 2021
Haywards Heath College, Harlands Road, Haywards Heath, West Sussex RH16 1LT, UK

NOVEMBER 27
Crystal Classics Winter Open Day 2021
No.1, The Old Coach Yard, East Coker, Somerset BA22 9HY, UK

 

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MINERAL WISH LIST

We also offer an additional service that enables you, as our customer, to contact us via orders@crystalclassics.co.uk with your mineral wish list to enhance your current collection, but are unable to find the right specimens on our website. We have 1000's of specimens in our general stock that do not appear online.

Author: JH
Categories: Updates

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